Over recent years the considerable increase in requests for current or voltage regulators, in particular those of the buck type, has lead to the trend of placing multiple output stages in parallel. The phase shift between the modules of 360°/N, where N is the number of the modules, entails an equivalent frequency on the output filter equal to Fs*N, where Fs is the frequency of the single module. The consequence of this is a decrease of the current ripple on the output filter, with the consequent possibility of using inductances with a lower value, and therefore less resistive and with a higher saturation current, without having to physically increase the working frequency penalizing the efficiency. In addition this phase shift leads to a considerable decrease of the Rms current on the input filter, with a consequent saving of capacitance.
As a consequence of the divisions of the output stage into multiple modules, a reaction loop has to be introduced that ensures the balance of the current between the modules themselves.
The solutions that have been adopted up to now are mainly synchronous (defined as voltage mode or current mode), as the phase shift between the modules can be easily obtained through the phase shift of the synchronization circuits.
Nevertheless, for several applications completely asynchronous reaction loops (defined as hysteretic in voltage, hysteretic in current, constant Ton, constant Toff) are preferable, but they can present problems with duty cycles exceeding 50%.